The upcoming Rust abstraction layer for the PWM subsystem uses a custom
`dev->release` handler to safely manage the lifetime of its driver
data.

To prevent leaking the memory of the `struct pwm_chip` (allocated by
`pwmchip_alloc`), this custom handler must also call the original
`pwmchip_release` function to complete the cleanup.

Make `pwmchip_release` a global, exported function so that it can be
called from the Rust FFI bridge. This involves removing the `static`
keyword, adding a prototype to the public header, and exporting the
symbol.

Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
---
 drivers/pwm/core.c  | 3 ++-
 include/linux/pwm.h | 6 ++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
index 0d66376a83ec350e0c3718959f4d794efd71595a..a33da3dff608fdff91251e5fd07b0dbd295be022 100644
--- a/drivers/pwm/core.c
+++ b/drivers/pwm/core.c
@@ -1600,12 +1600,13 @@ void pwmchip_put(struct pwm_chip *chip)
 }
 EXPORT_SYMBOL_GPL(pwmchip_put);
 
-static void pwmchip_release(struct device *pwmchip_dev)
+void pwmchip_release(struct device *pwmchip_dev)
 {
 	struct pwm_chip *chip = pwmchip_from_dev(pwmchip_dev);
 
 	kfree(chip);
 }
+EXPORT_SYMBOL_GPL(pwmchip_release);
 
 struct pwm_chip *pwmchip_alloc(struct device *parent, unsigned int npwm, size_t sizeof_priv)
 {
diff --git a/include/linux/pwm.h b/include/linux/pwm.h
index 8cafc483db53addf95591d1ac74287532c0fa0ee..d86061024b52172edf3845bf9252a966f120e365 100644
--- a/include/linux/pwm.h
+++ b/include/linux/pwm.h
@@ -485,6 +485,12 @@ int __pwmchip_add(struct pwm_chip *chip, struct module *owner);
 #define pwmchip_add(chip) __pwmchip_add(chip, THIS_MODULE)
 void pwmchip_remove(struct pwm_chip *chip);
 
+/*
+ * For FFI wrapper use only:
+ * The Rust PWM abstraction needs this to properly free the pwm_chip.
+ */
+void pwmchip_release(struct device *dev);
+
 int __devm_pwmchip_add(struct device *dev, struct pwm_chip *chip, struct module *owner);
 #define devm_pwmchip_add(dev, chip) __devm_pwmchip_add(dev, chip, THIS_MODULE)
 

-- 
2.34.1

Hello,

On Wed, Aug 20, 2025 at 10:35:36AM +0200, Michal Wilczynski wrote:
> The upcoming Rust abstraction layer for the PWM subsystem uses a custom
> `dev->release` handler to safely manage the lifetime of its driver
> data.
> 
> To prevent leaking the memory of the `struct pwm_chip` (allocated by
> `pwmchip_alloc`), this custom handler must also call the original
> `pwmchip_release` function to complete the cleanup.
> 
> Make `pwmchip_release` a global, exported function so that it can be
> called from the Rust FFI bridge. This involves removing the `static`
> keyword, adding a prototype to the public header, and exporting the
> symbol.
> 
> Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>

I still somewhat dislike this patch. Isn't it possible to make the rust
abstraction use the pointer that .release is set to when it calls
pwmchip_alloc()?

(I wouldn't further delay this series for this discussion, this can be
handled just fine at a later point in time.)

Best regards
Uwe

On Wed, Aug 20, 2025 at 10:35:36AM +0200, Michal Wilczynski wrote:
> The upcoming Rust abstraction layer for the PWM subsystem uses a custom
> `dev->release` handler to safely manage the lifetime of its driver
> data.
> 
> To prevent leaking the memory of the `struct pwm_chip` (allocated by
> `pwmchip_alloc`), this custom handler must also call the original
> `pwmchip_release` function to complete the cleanup.
> 
> Make `pwmchip_release` a global, exported function so that it can be
> called from the Rust FFI bridge. This involves removing the `static`
> keyword, adding a prototype to the public header, and exporting the
> symbol.
> 
> Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>
> ---
>  drivers/pwm/core.c  | 3 ++-
>  include/linux/pwm.h | 6 ++++++
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index 0d66376a83ec350e0c3718959f4d794efd71595a..a33da3dff608fdff91251e5fd07b0dbd295be022 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -1600,12 +1600,13 @@ void pwmchip_put(struct pwm_chip *chip)
>  }
>  EXPORT_SYMBOL_GPL(pwmchip_put);
>  
> -static void pwmchip_release(struct device *pwmchip_dev)
> +void pwmchip_release(struct device *pwmchip_dev)
>  {
>  	struct pwm_chip *chip = pwmchip_from_dev(pwmchip_dev);
>  
>  	kfree(chip);
>  }
> +EXPORT_SYMBOL_GPL(pwmchip_release);
>  
>  struct pwm_chip *pwmchip_alloc(struct device *parent, unsigned int npwm, size_t sizeof_priv)
>  {
> diff --git a/include/linux/pwm.h b/include/linux/pwm.h
> index 8cafc483db53addf95591d1ac74287532c0fa0ee..d86061024b52172edf3845bf9252a966f120e365 100644
> --- a/include/linux/pwm.h
> +++ b/include/linux/pwm.h
> @@ -485,6 +485,12 @@ int __pwmchip_add(struct pwm_chip *chip, struct module *owner);
>  #define pwmchip_add(chip) __pwmchip_add(chip, THIS_MODULE)
>  void pwmchip_remove(struct pwm_chip *chip);
>  
> +/*
> + * For FFI wrapper use only:
> + * The Rust PWM abstraction needs this to properly free the pwm_chip.
> + */
> +void pwmchip_release(struct device *dev);
> +
>  int __devm_pwmchip_add(struct device *dev, struct pwm_chip *chip, struct module *owner);
>  #define devm_pwmchip_add(dev, chip) __devm_pwmchip_add(dev, chip, THIS_MODULE)
>  
> 
> -- 
> 2.34.1

Reviewed-by: Elle Rhumsaa <elle@weathered-steel.dev>